The historical records, going back some more than 150 years, show tropical cyclones occurring in every month of the year both in the eastern Pacific and the Atlantic north of the equator. Despite this fact we have identified those months when tropical cyclone activity is more likely to take place to define what is known as the annual hurricane season. The eastern Pacific hurricane season will officially start this week on Tuesday 15 May 2012, while the Atlantic hurricane season must wait another couple of weeks to officially get started on 1 June 2012.
Although Mother Nature will be the one deciding when to generate tropical cyclones in either of these two basins, there have been numerous recent signs that some of the factors that contribute to cyclogenesis have began to get stronger and more organized, laying the foundation upon which a coincidence of favorable conditions could trigger a tropical cyclone at any time moving forward.
After being turned off for several months the tropical wave assembly line over Equatorial Africa is once again present generating waves of tropical activity that march to the west toward the eastern Atlantic and hurricane alley as shown in this color-enhanced infrared satellite image of 3 May 2012
Among those favorable signs we have recently seen the tropical wave assembly line over equatorial Africa become more prevalent to the north of the equator, while the belt of tropical activity to the north of the equator, which had been absent for several months, has started to once again show as a continuous region of rain and thunderstorms reaching from the eastern Atlantic all the way to the central Pacific and beyond. The tropical wave assembly line converts pulses of disturbed weather generated over the Indian Ocean into tropical waves consisting of regularly spaced cells of rain and thunderstorms that move west over Equatorial Africa to eventually emerge over the warm waters of the eastern Atlantic southward of the Cape Verde Islands, aiming for what is known as hurricane alley.
Composite satellite image of 3 May 2012 showing what is known as the 'belt of tropical activity' extending from the eastern Atlantic to the central Pacific ocean
A region of disturbed tropical weather marked by rains and thunderstorms over northern South America and the waters of the eastern Pacific Ocean off Central America are becoming prevalent as we approach the change of seasons
In addition to these early signs that hurricane seasons may not be that far off, other activity over the tropical regions of the northern western hemisphere mark the onset of other contributing factors, which include: (a) the development of a persistent region of disturbed weather, marked by rain cells and thunderstorms over the eastern Pacific Ocean to the west of Central America and South of Mexico, and (b) the continuing warming of surface waters over the tropical regions of the north Atlantic and north Pacific oceans.
Both of these indicate the heat content in the tropical oceans continues to increase, providing a source of energy for potential tropical cyclone generation in the future. On the other hand the persistent region of tropical activity over the eastern Pacific marks a sub-basin where cyclogenesis takes place.
Satellite-based map showing sea surface temperatures over portions of the Pacific and Atlantic oceans on 12 May 2012 that include a vast area of 30+ Celsius temperatures to the west of Central America
In case more signs were needed, today Sunday 13 May 2012 there are two new signals provided by Mother Nature, one in the Atlantic and one in the eastern Pacific, which tell us to pay attention and keep watching for potential further development.
Water vapor satellite image of the Atlantic on 13 May 2012 showing a distinct region of low pressure just south of the Azores Islands that warrants close attention
Color-enhanced infrared satellite image of 13 May 2012 showing the same potential cyclonic activity near the Azores Islands in the Atlantic
The weather system shown on the images above was located some 500 kilometers to the southwest of the Azores and moving toward the northeast. While the system is showing some cyclonic tendencies, it is tracking over a region of the Atlantic with cooler surface waters although the surrounding environment is one experiencing low wind shear, which might be conducive for some better organization and further development of this system. Both of these regional conditions are illustrated by the images below:
Satellite-based map of sea surface temperatures on 12 May 2012 showing the progressively cooler surface waters ahead of the weather system approaching the Azores
Wind-shear superimposed on a satellite image showing the Atlantic on 13 May 2012 and the area of low wind-shear around the weather system of interest near the Azores Islands
The other signal that has emerged in the early hours of Sunday 13 May 2012 is over the eastern Pacific Ocean some 500 kilometers southwest of Acapulco, Mexico and 1,500 kilometers west of Guatemala. The signal identifies a region of low pressure and disturbed weather moving over rather warm surface waters in a low wind-shear environment, which provide rather favorable conditions for further development and potential strengthening over the next 12-24 hours. This is clearly a system to be watched, which is being monitored closely by NOAA’s National Hurricane Center.
Satellite image of 13 May 2012 showing water vapor in the atmosphere over the eastern Pacific Ocean near the coast of Mexico and Central America where an area with potential for cyclonic development is clearly visible
Color-enhanced infrared satellite image of 13 May 2012 showing the same region of the eastern Pacific Ocean seen in the image to the left
Elevated sea surface temperatures and low wind-shear conditions, which create a favorable environment for the system we are following over the eastern Pacific Ocean near the western coastline of Mexico, are illustrated by the satellite images below:
Satellite-based map of sea surface temperatures on 12 May 2012 showing a large region of waters at temperatures ranging from 28 to 32 Celsius near the coast of Mexico where we are monitoring a weather system with potential for cyclonic development
Satellite image of 13 May 2012 showing the eastern Pacific Ocean off Mexico and Central America and current wind-shear conditions over the area where we are monitoring a potentially cyclonic weather system\
This specific disturbed weather system over the eastern Pacific is moving approximately west by northwest, and it is being given a 50% probability for further development by the National Hurricane Center, which is monitoring it closely. Could this be the first tropical cyclone of the Eastern Pacific 2012 hurricane season, right on target or just a sampler of things to come? Only time will tell, keep watching, pay attention! Be prepared!! Mitigate!!!
Related to this, the 26th Annual Governor’s Hurricane Conference gets under way tomorrow Monday 14 May 2012 at the Fort Lauderdale Broward County Convention Center. While the conference will be officially inaugurated in the early afternoon on Wednesday 16 May 2012, a full program of training sessions starts on Monday morning. It will be interesting to see if Mother Nature will provide a relevant backdrop in terms of tropical cyclone activity.
One of the ‘new’ signals mentioned in this posting, the low pressure disturbed weather cell off the coast of Mexico in the Eastern Pacific less than 24 hours later has reached tropical depression status, in the morning of Monday 14 May 2012. As this system moves west by northwest over rather warm surface waters in a favorable atmospheric environment, it appears to be strengthening further and may become a tropical storm within the next 12 to 24 hours. Should this projected development take place, this system would become the first tropical cyclone of the 2012 Eastern Pacific hurricane season, which officially starts tomorrow Tuesday 15 May 2012!
Right on target! The tropical depression we have been monitoring over the eastern North Pacific has continued to strengthen during the early evening hours this Monday 14 May 2012, and it has now reached Tropical Storm conditions under the name of ALETTA, the first named storm of the 2012 eastern Pacific hurricane season, which officially starts tomorrow Tuesday 15 May 2012. Aletta is moving generally westward with maximum sustained winds of 65 kph [40 mph]. While tropical storm Aletta continues its progress over the open ocean, there are some large cells of disturbed weather following on its tracks to the west of Central America that may warrant attention.